The wickedness of Anders Behring Breivik

I defer to Dr Paul McMahon's professional judgment regarding the particular case of Anders Behring Breivik's insanity (Letters, 27 August), but it prompts so many questions. If those who commit atrocious acts are mad, who is bad?

Breivik's vile philosophy is shared by many. Are they all mad, or do we "sane" people simply deem them so? Without falling for the original-sin view of the world, can't we accept that some people, from choice not psychosis, believe wicked things and perform wicked deeds? Isn't it a feat of circular reasoning to label people mad because they have perpetrated appalling crimes? Doesn't it let us off the hook to label them insane, so we do not need to address their ideology and its breeding ground?

At the other extreme, what of those who dedicate their lives to others and sacrifice themselves for the greater good? Are they insane? Perhaps we need philosophers, not psychiatrists, to answer such questions.Susan SeagerLondon

• I beg to disagree (partially) with Paul McMahon. Breivik's paranoid delusions seem hardly caused by the treatable illness we term paranoid schizophrenia. I concede that they are evidence of some mental aberration. But his concise, "pure" paranoid delusions, which he logically defended, have proved treatment-resistant.

The crucial point to me is that Breivik was oblivious as to how his drastic crime would advance his political aims – of limiting Muslim immigration and of keeping Norwegians from intermarrying – except in his claim that the youngsters he killed were "cultural Marxists" whose political activism would adulterate pure Norwegian blood. Similar irrational views were promoted 70-80 years ago in the Nazi era with regard to Aryan blood being contaminated by Jews, Gypsies and Slavs. I cannot recall these being regarded as occasioned by treatable mental illness, but only as totally evil.Dr Susi Shafar(Retired consultant psychiatrist), Nelson, Lancashire